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Sub-resolution assist features (SRAF) insertion using mask synthesis process based on pixel-based mask optimization schemes has been studied in recent years for various lithographical schemes, including 6% attenuated PSM (AttPSM) with off-axis illumination. This paper presents results of application of the pixelbased optimization technology to 6% and 30% AttPSM mask synthesis. We examine imaging properties of mask error enhancement factor (MEEF), critical dimension (CD) uniformity, and side-lobe printing for random contact hole patterns. We also discuss practical techniques for manipulating raw complex shapes generated by the pixel-based optimization engine that ensure mask manufacturability.

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